1. Field of the Invention
This invention relates to cyclone separators, and more particularly to cyclone separators with influent guide blades.
2. Description of The Prior Art:
Cyclone separators are used for various purposes, for instance, for centrifugally separating or collecting solid particles of foreign matter from a fluid by whirling them in vortexes of the fluid, for classifying solid particles in a fluid according to the mass scales of the individual particles, or for effecting heat exchange between a solid and a gas by contacting them with each other or during separation thereof. The cyclones are used independently or in combination with other equipment depending upon the purposes for which they are intended to serve, including:
(a) A separator used at the terminal end of a pneumatic particle transfer line.
(b) A separator used at the terminal end of a drifted air-drying line for coal or the like.
(c) A cyclone separator used in a closed-circuit type pulverizing equipment for various ores or other raw materials.
(d) A heat exchanger for preheating raw cement powder, aluminum hydroxide powder or powdery limestone or other material prior to calcining.
There have thus far been made various studies with objectives of reducing the pressure losses and improving the separation efficiency in the cyclone separators of the above-mentioned classes. However, these objectives are contrastively related with each other since there is a general tendency that a cyclone separator with a small pressure loss is low in separation efficiency or vice versa. Among the known cyclone constructions, the cyclone separator which has an influent guide blade at an inlet duct is regarded as having a relatively high separation efficiency in spite of its low pressure loss although not satisfactorily high enough. The pressure loss and collecting efficiency by a cyclone separator of a standard or plain construction have been explained to a practical extent by theoretical analysis. However, no sufficient analysis has ever been made of the behaviors of fluid flows within a cyclone of a special construction like a cyclone with an influent guide blade. Referring to the accompanying drawings and first to FIGS. 1 and 2, there is shown a conventional cyclone of the standard type which is not provided with an influent guide blade. the cyclone has a straight cylindrical portion 1 and an inverted conical portion 2 which is formed contiguously below the straight cylindrical portion 1 and has a downwardly reducing sectional area twoard an outlet 3, which is provided at its lower end for the withdrawal of separated solid foreign material. The upper end of cylindrical portion 1 is closed with a ceiling wall 4 which is centrally provided with an opening to receive the lower end portion of an exhaust duct 5 in upper cylindrical portion 1. An inlet duct 6 is tangentially or circumferentially connected to the upper end of straight cylindrical portion 1 to feed a fluid containing solid particles to be separated or classified. The influent of mixed phase is whirled between exhaust duct 5 and the inner wall surface of straight cylindrical portion 1 to form a vortex 8 which is gradually lowered and finally reversed at the converged lower end of the conical portion to form a central axial flow, leaving the cyclone through exhaust duct 5. On the other hand, the solid particles in vortex 8 are separated or classified under the influence of the centrifugal force toward and along the inner wall surfaces of the straight cylindrical portion and lower conical portion 2 for discharge through outlet 3.
This type of cyclone suffers from not only an insufficient separation efficiency but also a large pressure loss of the fluid, requiring employment of a suction blower of a large capacity. Therefore, there has been a strong demand for the improvement of the separation efficiency and the reduction of the pressure loss. The large pressure loss in the above-described cyclone is considered to occur for the following reason. As indicated by arrows in FIGS. 1 and 2, the fluid which has been whirled around exhaust duct 5 is impinged obliquely against the fresh influent fluid from inlet duct 6, pushing the influent fluid toward the inner peripheral wall of the cyclone to cause "contracted flow". As a result, the velocity of flow on the inner peripheral wall of the straight cylindrical portion is increased as compared with that of the influent fluid in inlet duct 6, increasing the pressure loss due to friction against the inner peripheral wall of the cylindrical portion.
FIGS. 3 and 4 illustrate a convention cyclone separator with an influent guide blade. More particularly, the cyclone is provided with an influent guide blade 10 which is projected on the extension of and at the same height as the inner side wall of the inlet duct. As shown in FIG. 4, the influent fluid which has been admitted through inlet duct 6 and whirled around the lower end of exhaust duct 5 is impinged against influent guide blade 10 and thereby directed in a direction substantially parallel with the fresh influent fluid. The provision of the inlet guide blade thus prevents the occurrence of contracted flow and the increase of the flow velocity on the inner peripheral wall is increased due to the contracted flow as shown in FIG. 1, the pressure loss is increased due to the increased number of revolutions of the fluid. In this regard, influent guide blade 10 also contributes to reduce the number of revolutions of thefluid and hence the pressure loss.
Thus, the influent guide blade 10 has a function of effectively reducing the pressure loss but has a problem in that the separation efficiency of solid particies is sacrificed. Namely, the conventional inlet guide blade fails to provide a perfect improvement.
Under these circumstances, the present invention is directed to improving both the pressure loss and separation efficiency by an extensive study on their relation with the shape, dimensions and mounting position of the influent guide blade.